Large seafaring vessels are commonly powered by large internal combustion engines that require continuous cooling under various operating conditions, such as during high speed cruising, low speed operation when approaching ports, and full speed operation for avoiding bad weather, for example. Existing systems for achieving such cooling typically include one or more pumps that draw sea water into heat exchangers onboard a vessel. The heat exchangers are used to cool a closed, fresh water cooling loop that flows through and cools the engine(s) of the vessel and/or other various loads onboard the vessel (e.g., air conditioning systems).
A shortcoming associated with existing sea water cooling systems such as that described above is that they are generally inefficient. Particularly, the pumps that are employed to draw sea water into such systems are typically operated at a constant speed regardless of the amount of sea water necessary to achieve sufficient cooling of the associated engine. Thus, if an engine does not require a great deal of cooling, such as when the engine is idling or is operating at low speeds, or if the sea water being drawn into a cooling system is very cold, the pumps of the cooling system may provide more water than is necessary to achieve sufficient cooling. In such cases, the cooling system will be configured to divert an amount of the freshwater in the freshwater loop directly to the discharge side of the heat exchangers, where it mixes with the rest of the freshwater that flowed through, and was cooled by, the heat exchangers. A desired temperature in the freshwater loop is thereby achieved. However, the system does not often require the full cooling power provided by sea water pumps driven at constant speed (hence the need to divert water in the fresh water loop). A portion of the energy expended to drive the pumps is therefore wasted. Thus, there is a need for a more efficient sea water pumping system for use in heat exchange systems servicing the marine industry.